Dimmable ballasts having a large input and output voltage range are increasingly being demanded in light emitting diode applications. Therefore, a settable power range which significantly exceeds a settable power range of a customary ballast for fluorescent lamps is demanded in light emitting diode applications. Although in the case of fluorescent lamps, too, there are ballasts which can dim different loads in each case down to a partial power of approximately 1%, said ballasts must additionally always apply a basic power for the heating of the electrode filaments of the fluorescent lamps, such that converter stages of the ballasts always have to apply a corresponding minimum power that is rarely less than 10% of the rated power. This is different in the case of ballasts for solid-state lighting (SSL). Here a power range that can be set to 100 mW or to a few percent of the rated power is often demanded. In this context, US 2012/0286686 A1 discloses a lighting device for a solid-state light source.
SSL ballasts often include energy converters, or converters, which are operated in switching operation, that is to say are clocked. In order to be able to generate the very low powers, the converters are often operated at very high frequencies. This not only causes high switching losses, but furthermore can also cause problems with regard to electromagnetic compatibility (EMC).
Furthermore, operation at high frequencies requires power components suitable therefor and, if appropriate, corresponding circuitry measures, which are associated with high costs. For this reason, such converters for providing very low powers, for example in the boost operating mode or else in the buck operating mode, below a predefined comparison power, are operated in a so-called burst operating mode. The burst operating mode is distinguished by the fact that the converters remain switched on for a few clock cycles and are then deactivated for a longer time, that is to say a plurality of clock cycles. The burst operating mode proves to be disadvantageous insofar as evolution of noise as a result of frequencies in the audible range that arise from the sequence of the burst packets can be the consequence and an intermediate circuit of such a converter can have increased ripple on account of operation following the principle of a two-point controller.